The overall objective of the proposed research is to increase our understanding of spoken language comprehension. The research focuses specifically on the very early stages of comprehension, during which the listener analyzes the speech signal so as to recover the prelexical linguistic structure of the utterance - the sequences of phonetic segments (consonants and vowels) that comprise the lexical items of a language. Over the years, considerable emphasis has been placed on the abstract nature of the prelexical representations of speech. Indeed, a widely held assumption in the speech perception literature for many years was that during the course of processing, listeners derive an abstract phonetic representation and, in the course of doing so, discard information about the fine-grained detail of the speech signal. However, more recent research has shown that the representations of speech are much richer than this emphasis on abstract entities would suggest, and that listeners retain in memory a substantial amount of fine-grained acoustic-phonetic information. This shift in emphasis away from abstract representations and toward representations that code detailed information about acoustic-phonetic form represents a major change in the field. The proposed research builds on findings from our current research program to investigate the nature of the fine-grained prelexical representations of speech and the way in which acoustic-phonetic fine-structure influences selected aspects of processing. Three related sets of studies are proposed. The first set investigates constraints on how qualitatively different kinds of contextual factors affect prelexical processing; the second set investigates how variation in acoustic-phonetic form due to talker characteristics affects prelexical processing; and the third set investigates how variation in acoustic-phonetic form due to a foreign accent affects prelexical processing. The proposed research will provide fundamental information on the role of acoustic-phonetic fine-structure in speech perception. Such information will help provide a firm basis from which to study both the development of speech processing abilities during the first years of life, and those aspects of speech, language, and hearing disorders that involve acoustic-phonetic processing.